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INDUSTRIAL AND ENGINEERING CHEMISTRY
aluminum paint, it will be noted that every zinc yellow panel is rusted, whereas every ZTO chromate panel except one is free from corrosion. Similar results were obtained in exposures a t mean-tide level in Miami. These panels, like the former Florida set, were of sandblasted, noncopper-bearing, black iron. After the entire surface was primed, the left half of each panel was given a finish coat of aluminum paint. The results after 3-month exposure and pertinent formulation data are shown in Figure 16. The superiority of ZTO chromate over commercial zinc yellow is again indicated and is most evident in the twocoat sections of the panels. These show considerable blistering and rusting for the three zinc yellow tests, while the corresponding ZTO chromate panels show only slight failures. It is interesting to note that under these extremely severe exposure conditions, the single-coat tests showed improvement with increasing ZTO chromate content, whereas with zinc yellow the results became poorer. In addition, exhaustive exterior exposure tests are under way under a variety of service conditions, including industrial atmospheres. Although some of these tests have been under exposure for about three years, failures have not yet progressed to a point where reliable conclusions can be drawn. However, all of the ZTO chromate films are still in perfect condition, and it seems apparent that satisfactory metal protection can be obtained by the use of paint systems comprising suitably formulated ZTO chromate primers and a finishing paint adapted to the particular service conditions. This new chromate pigment makes possible the formulation of metal protective paints having the outstanding rust inhibiting characteristics of zinc yellow without the necessity of resorting to synthetic resin vehicles to obtain films of satisfactory water resistance. Because of the good water
Vol. 34, No, 3
resistance that can be obtained with ZTO chromate primers prepared with ordinary linseed oil vehicles, the superior corrosion-inhibiting action associated with chromates can now be taken advantage of more generally in the field of metal finishing. Fortunately the pigment possesses a low specific gravity, so that ZTO chromate primers do not add unnecessarily to the dead load of large structures such as bridges and ships.
Literature Cited (1) Am. SOC.for Testing Materials, Proceedings, 15, I, 214 (1915). ( 2 ) Anonymous, Steel, 98,43 (June 1, 1936). (3) Bancroft, W. D., and Porter, J. D., J . Phys. Chem., 40, 37 (1936). (4) Bannister, L. C., and Evans, U. R., J. Chem. SOC.,1930, I, 1m i
Barti,,‘G.,2.Physik, 87,399 (1934). Burns, R. M.,and Haring, H. E., Trans. Electrochem. Soc.,
(11) (12) (13) (14) (15) (16)
69, 169 (1936). Burns, R. M., and Schuh, A. E., “Protective Coatings for Metals”, A. C. S. Monograph 79, pp. 306-12, Yew York, Reinhold Pub. Corp., 1939. Edwards, J. D. (to Aluminum Co. of Am.), U. S. Patents 1,946,151-2 (Feb. 6, 1934). ENG.CHEM.,27, 1145 Edwards, J. D., and Wray, R. I., IND. (1935). ENG.CHEM., ANAL.ED.,7, Edwards, J. D., and Wray, R. I., IND. 5 (1935). McCloud, J. L., IND. ENG.CHEM.,23,1334 (1931). May, R., J. Inst. Metals, 40, 141 (1928). Mellor, J. W., “Comprehensive Treatise on Inorganic and Theoretical Chemistry”, Vol. XI, p. 279 (1931). Penick, D. B., Rm. Sci.Instruments, 6, 115 (1935). ENG.CHEM.,30, 1152 (1938). Speller, F. N., IND. Winston, A. W., Reid, J. B., and Gross, W. H., Ibid., 27, 1333 (1935).
PRESENTED before the Division of Paint, Varnish, and Plastics Chemistry a t the 102nd Meeting of the AMERICANCHEMICAL SOCIETY, Atlantia City, N.J.
Molecular Volume of Liquid Alkanes at Corresponding Temperatures
GUSTAV EGLOFF AND ROBERT C. KUDER
Universal Oil Products Company, Chicago, Ill.
I
N ATTEMPTS to find comparative conditions such that
the molecular volume in homologous series is an additive function, the boiling Point (7, 10) and the melting Point (8, 11) have been used as temperatures of comparison- The use of these temperatures derives from the fact that for the members of a series either temperature is approximately a constant fraction of the respective critical temperatures, the desirability of comparison a t equal reduced temperatures being recognized from the theory Of states* The best data show, however, that in the case Of hydrocarbons a t their boiling points (7) the molecular volume of homologs is not a strictly additive function, and that in the case of aliphatic hydrocarbons at their melting points (8) the situation is complicated by the effectsof molecular and alternating melting points.
The failure of the boiling point or the melting point as a comparison temperature in the quest of additive molecular volume may be ascribed t o a t least two factors. The first factor is the approximation involved in the Guldberg relation between boiling points and critical temporetures; the inconstancy of the ratio of boiling point t o critical temperature is As Table I readily discerned from the work of Young shows,the melting point is a variable reduced temperature in the case of normal The second factor is the failure of the theory of corresponding states itself to m7i1son and Bahlke ( l a )pointed out that the Plot of reduced volume (in the liquid state) against the reduced temperature “does not give one line for all the normal paraffin hydrocarbons, but . . . a t any one ‘reduced tempera-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
March, 1942
Thus by combining Equations 2 and 3 with Equation 1, t h e molecular volume equation may be calculated for any reduced temperature. These equations hold for the normal alkanes from ethane to octane, inclusive (only the very first member of the series, methane, is slightly inconsistent). The equations were calculated from the molecular volumes a t the reduced temperatures 0.35, 0.40, 0.45, 0.50, 0.55, and 0.60 by the method of least squares; and they reproduce the data at these temperatures with an average percentage deviation of 0.12 per cent (standard error of estimate, 0.15 ml. per mole; average deviation regardltxs of sign, 0.12 ml. per mole).
The molecular volume is an additive function at any reduced temperature between the melting points and the boiling points of the normal alkanes from ethane to octane, inclusive, with no complications from the alternating factor. The equations, V=a+bn a = 9.43
+ 10.24 TR + 1.765 TR f 10.00 Ti
b = 14.912
TABLE^ 111. MOLECULAR VOLUME AT TR =
reproduce the data with an average percentage deviation of about 0.12 per cent.
t,
n
c.
Vobsvd.,
- 120.44
ture’ (T/T,) the ratio V1/VCtends to decrease slightly with increasing molecular weight”. To overcome the faults of the melting and boiling points as corresponding temperatures, this study of molecular volume was made a t a series of exactly equal reduced temperatures. The normal alkanes are the only hydrocarbon series of any length for which the critical temperatures have been determined; the values chosen from the recent literature are shown in Table 11. The molecular volumes a t various fractions of the critical temperatures were calculated by interpolation and extrapolation of published density data (B), with the exception of the values for butane. For this hydrocarbon the densities were calculated from the equation: Of = 0.6013
37
- 0.001016t
This equation reproduces with an error less than the experimental error every value of the density of butane below its normal boiling point as determined by Coffin and Maass (6).
51.16 69.42 87,69 106.11 124.04 142.49 160.97
-88.18 -60.58 -38.0 -19.2 -3.08 11.5
Vaalcd.
MI. per mole 51.14 69.43 87.73 106.02 124.31 142.61 160.90
AT7
-0.02
0.01 0.04 -0.09 0.27 0.12
-0.07
TABLE IV. EFFECT OB REDUCED TEMPERATURE ON EQUATION 1 TR 0.35 0.40 0.45 0.60 0.55 0.60
a, Ml./Mole 13.01 13.63 14.04 14.65 16.06 15.57
b, Ml./Mole per CHI
16.765 17.218 17.731 18.294 18.908 19.571
As an example of the resulta produced by these equations, Table 111 shows the observed and calculated molecular volumes a t half the critical temperatures. The variation in the methylene volume increment between temperatures near the melting points and temperatures near the boiling points is indicated in Table IV. Literature Cited Beattie, J. A., and Kay, W. C., J. Am. Chem. Soc., 59, 1688-7 (1937).
Beattie, J. A., Poffenberger, N., and Hadlock, C., J. C h m . Methane Ethane Propane Butane
0.473 0.332 0.232 0.326
0.585 0.605 0.625 0.642
Pentane Hexane Heptane Octane
0.305 0.363 0.338 0.380
0.657 0.673 0.688
0.700
TEMPERATURES OF NORMAL ALKANES TABLE 11, CRITICAL Hydrooarbon Methane Ethane Propane Butane Pentane Hexane Heptane Octane
TO, K. 191.03 305.43 369.97 425.17 470.4 508.0 640.17 569.4
Referenoe Keyen Taylor Smith (8) Beattfe Su dmard (1) Beatti: Pokenber er Eadlock Beattie: Simard, &a (3) Young IS Young Beattie and K a y (0
LJ
Youtlg
Phys., 3,96-7 (1935). Beattie, J. A., Simard, G. L., and Su,G.-J., J. Am. Chem. SOC., 61,26-7 (1939). Beattie, J. A,, Su, G . J . , and Simard, G. L., Ibid., 61, 924-5 (1939). Coffin, C. C.,and Maass, O., Ibid., 50, 1427-37 (1928).
Egloff, G., “Physical Constants of Hydrocarbons”. Vol. I, New York, Reinhold Pub. Corp., 1939. Egloff,G., and Kuder, R. C., J. Phys. Chem., 45, 836-45 (1941); J. Inst. Pelroleurn Tech., 27,260-74 (1941). Egloff, G.,and Kuder, R. C., paper at A. C. S. meeting, St. Louis, 1941. Keyes, F. Q., Taylor, R. S.,and Smith, L. B., J. Math. Phys., 1, 211-42 (1922).
Kopp, H., Ann., 41,79-89 (1842); 96,153-85 (1855). Le Bas, G.,J. Chem. SOC.,91, 112-5 (1907); PhiE. M ~ Q . ,[el
(in
16. 60-92 (1908).
Wilson, R. E:,and Bahlke, W. H., IND. ENQ.CHEW.,16,116-22
It was found that a t any given reduced temperature,
TR,
between the melting point and the boiling point a t atmospheric pressure the molecular volume is a truly additive function; that is, it may be expressed as a linear function of the number of carbon atoms, n,in the molecule: V=a+bn
+
+ 1.765 TR f 10.00 Ti
P R E U ~ N Tbefore B D the Division of Petroleum Chemistry at the 102nd Meeting of the AM~BICAN CHEMICAL SOCIETY, Atlantic City, N. J.
(1)
Furthermore, the parameters a and b are simple functions of the reduced temperature: a = 9.43 10.24 T R (2) b = 14.912
(1924).
Young, S.,Sci. Proc. Roy. Dublin SOC.,12,374-443 (1910). Ibid., 15, 93-8 (1916).
(3)
Expansion of the Trona Enterprise-Correction An error a pears in literature citation (7)of the above artiole by G. Ross Zobertson in the February number pa e 137. The U. S. Patent issued t o Gale and Pearson should be 80.2,251,353 (Aug. 5, 1941).
